1. Field of the Invention
This invention relates generally to the use of anti-CD18 antibodies for treating stroke. In particular, it relates to the use of anti-CD18 antibodies for improving clinical outcome by increasing cerebral blood flow and/or reducing infarct size in focal ischemic stroke caused by obstruction of a main cerebral artery.
2. Description of Related Art
Stroke is a general term for acute braindamage resulting from disease of blood vessels. This presents a serious problem to society, with about 500,000 people dying from or becoming permanently disabled by stroke in the United States each year. Stroke can be classified into two main categories: hemorrhagic stroke (resulting from leakage of blood outside of the normal blood vessels) and ischemic stroke (cerebral ischemia due to lack of blood supply); this application is primarily concerned with the latter.
The three main mechanisms of ischemic stroke are thrombosis, embolism and systemic hypoperfusion (with resultant ischemia and hypoxia). In each of these types of stroke, the area of the brain that dies as a result of the lack of blood supply thereto is called an infarct. Obstruction of a cerebral artery resulting from a thrombus which has built up on the wall of a brain artery is generally called cerebral thrombosis. In cerebral embolism, the occlusive material blocking the cerebral artery arises downstream in the circulation (e.g. an embolus is carried to the cerebral artery from the heart). Because it is difficult to discern whether a stroke is caused by thrombosis or embolism, the term thromboembolism is used to cover both these types of stroke. Systemic hypoperfusion may arise as a consequence of decreased blood levels, reduced hematocrit, low blood pressure or inability of the heart to pump blood adequately.
When symptoms of stroke last less than 24 hours and the patient recovers completely, the patient is said to have undergone a transient ischemic attack (TIA). The symptoms of TIA are a temporary impairment of speech, vision, sensation or movement. Because a TIA is often thought to be a prelude to full-scale stroke, patients having suffered a TIA are candidates for prophylactic stroke therapy with anticoagulation agents (e.g., coumarin and heparin) or antiplatelet agents (such as aspirin and ticlopidine) for example. Thrombolytic agents, such as tissue plasminogen activator (t-PA), have been used in the treatment of thromboembolic stroke. These molecules function by lysing the thrombus causing the ischemia. Such drugs are believed to be most useful if administered as soon as possible after acute stroke (preferably within 3 hours) in order to at least partially restore cerebral blood flow in the ischemic region and to sustain neuronal viability. In that such drugs exacerbate bleeding, their use in hemorrhagic stroke is contra-indicated.
A family of adhesion glycoproteins present on leukocytes is called the integlin family. This integrin family includes LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18) and p150,95 (CD11c/CD18). A further member of this family CD11d/CD18 has recently been reported. Danilenko et al., J. Immunol. 155:35-44 (1995). Each of these heterodimers has a unique .alpha.-chain (CD11a, b, c or d) and the invariant .beta.-chain (CD18). CD18 integrins located on leukocytes may bind to intercellular adhesion molecule-1 (ICAM-1) which is expressed on vascular endothelium and other cells, thereby mediating leukocyte adhesion and transendothelial migration.
It has been noted that CD11a and CD18 are upregulated in leukocytes from patients who have undergone ischemic stroke or a TIA. Kim et al., J. Neurolog. Sci. 128(1):45-50 (1995). Schroeter et al, J. Neuroimmunology 55(2):195-203 (1994) found that increased expression of ICAM-1 on vessels and leukocytes occurred following cerebral ischemia induced by permanent occlusion of the middle cerebral artery (MCA) in the rat.
The role of cell adhesion molecules in brain injury following transient MCA occlusion in the rat has been studied (Matsuo et al., Brain Research 656:344-352 (1994)). Matsuo et al. inserted a nylon thread from the lumen of the external carotid artery (ECA) to that of the right internal carotid artery (ICA) in order to occlude the origin of the right MCA. The occlusion was transient; after 1 hour, the nylon thread was removed to allow complete reperfusion of the ischemic area via the right common carotid artery (CCA). Anti-CD11a (WT1), anti-CD18 (WT3) and anti-ICAM-1 (1A29) antibodies were administered before ischemia and immediately after reperfusion. These researchers found that treatment with individual antibodies against cell adhesion molecules reduced edema formation, infarct size and neutrophil accumulation following reperfusion.
Others have investigated the effects of antibodies against cell adhesion molecules in such transient stroke models. Zhang et al., Brain Research 698:79-85 (1995) studied the effects of anti-CD11b and anti-CD18 monoclonal antibodies in ischemia/reperfusion injury, wherein the antibodies were administered upon and after transient MCA occlusion (the origin of the MCA was transiently blocked with a surgical nylon filament). Mori et al., Stroke 23(5): 712-718 (1992) studied the effects of the anti-CD18 IB4 antibody in their baboon model of reversible MCA occlusion. In this model, arterial obstruction was achieved by inflating an extrinsic MCA balloon to 100 .mu.l. Reperfusion occurred following balloon deflation. See, also, Chopp et al., Stroke 25(4):869-876 (1994) and Chen et al., Annals of Neurology 35(4): 458-463 (1994) concerning an anti-CD11b antibody in a transient cerebral ischemia model. Chopp et al, and Chen et al., advanced a surgical nylon suture into the ICA to block the origin of the MCA. Reperfusion was accomplished by withdrawing the suture until the tip cleared the ICA lumen.
Takeshima et al., Stroke, 23(2):247-252 (1992) found that the anti-CD18 antibody 60.3 did not afford protection from severe focal ischemia and reperfusion in a transient focal cerebral ischemia model in cats. Takeshima et al. used a microvascular clip to occlude the MCA and occluded CCAs by tightening previously placed ligatures.
Lindsberg et al. J. Neurosurq. 82:269-277 (1995) subjected rabbits to severe spinal cord ischemia (by inflating the balloon of a catheter tip which had been introduced in the abdominal aorta) followed by 30 minutes of reperfusion at which time either: (1) vehicle, (2) anti-CD18 antibody, or (3) anti-CD18 antibody and platelet-activating factor (PAF) antagonist were administered to the animals. Recovery of motor function was improved by the anti-CD18 antibody, but no further improvement was induced by the PAF antagonist.
It has been observed that while an anti-CD18 antibody reduced neurologic deficits in the reversible spinal cord model (involving a snare ligature occluding device), it was unable to do so in an irreversible microsphere model. Clark et al., Stroke 22(7): 877-883 (1991). Clark et al. conclude that leukocytes potentiate their effect in central nervous system injury via reperfusion injury. With respect to anti-CD11b antibodies, Chopp et al., Stroke 25(1):267 (1994) report that benefit from administration of such antibodies was observed under conditions of transient, but not permanent, MCA occlusion in rats. See, also, Jiang et al., Neuroscience Research Communications 15(2):85-93 (1994). Clark et al., J. Neurosurg 75(4):623-627 (1991) also observe that while anti-ICAM-1 produced a significant reduction in neurological deficits in the reversible spinal cord ischemia model, such therapeutic benefit was not seen in the irreversible brain ischemia model. Similar findings in relation to anti-ICAM-1 antibodies have also been reported by Zhang et al., Stroke 26(8):1438-1442 (1995).
Bowes et al., Neurology 45:815-819 (1995) evaluated the ability of monoclonal antibodies directed against ICAM-1 and CD18 to enhance the efficacy of thrombolysis in a rabbit cerebral embolism stroke model. In this model, numerous small blood clots (formed by fragmenting a clot with a tissue homogenizer) were injected into the rabbit's carotid circulation in order to achieve embolization. Neurologic function in each animal was evaluated 18 hours following embolization on a three point scale: (1) normal activity; (2) abnormal activity; or (3) death. The amount of clot necessary to produce permanent neurologic damage in 50% of the rabbits (ED.sub.50) was determined for each treatment group. Bowes et al., found that when administration of anti-CD18 or anti-ICAM-1 was delayed until 15 or 30 minutes after embolization, a statistically significant improvement in neurologic function was not observed. See also Bowes et al., Experimental Neurology 119(2):215-219 (1993) in relation to earlier work by this group regarding anti-ICAM-1 and t-PA in their rabbit cerebral embolism stroke model.
Bednar et al., Stroke 23(1):152 (1992) describe a rabbit model of thromboembolic stroke wherein the arterial occlusion (an autologous blood clot delivered to the anterior cerebral circulation) is not removed during the experiment. Rabbits received either anti-CD18 antibody IB4 (1 mg/kg), or vehicle, 30 minutes following the thromboembolic event. Following embolization, the animals were studied for a total of 4 hours, including an initial 45 minutes of systemic hypotension. No statistically significant difference in cerebral blood flow (CBF) or infarct size between IB4 and vehicle treated animals was seen. However, IB4 did attenuate intracranial hypertension in this model.
It is an object of the present invention to provide a method for improving clinical outcome in acute ischemic stroke by increasing cerebral blood flow and/or reducing infarct size. Furthermore, it is an object of the invention to provide an alternative to thrombolytic therapy for treating thromboembolic stroke, particularly where thrombolytic therapy has been unsuccessful or is contra-indicated, as is the case where the patient to be treated is taking aspirin, or where the time delay from the onset of stroke to diagnosis is such that thrombolytic therapy is not recommended. Other objects will be apparent from the description which follows.